1. Field of the Invention
The present invention generally relates to an apparatus for controlling a variation in torque of an internal combustion engine, and more particularly to a torque variation control apparatus which controls a predetermined parameter of the internal combustion engine so that the amount of intercycle variation in torque of the internal combustion engine is maintained within an allowable torque variation amount range.
2. Description of the Related Art
As is well known, various apparatuses have been proposed which intend to improve the fuel economy of an internal combustion engine and reduce the amount of nitrogen oxides (NOx) therein. Japanese Laid-Open Patent Publication No. 2-176138, for example, discloses an apparatus which measures the amount of intercycle variation in torque of the internal combustion engine and controls a predetermined engine control parameter so that the measured intercycle torque variation amount becomes equal to a target torque variation amount suitable for a current engine operating condition. Some features of conventional methods are, for example, that the air-fuel ratio is controlled so that a mixture of air and fuel is as lean as possible, or that an exhaust gas recirculation system is controlled so that an increased amount of exhaust gas is fed back to an intake manifold.
However, the conventional torque variation control apparatus disclosed in the above Japanese publication has the following disadvantage. If the engine operating condition changes during a procedure for generating a torque variation amount which is based on an average (or weighted average) of intercycle torque variation amounts obtained by sampling for a predetermined number of cycles of the engine and which is to be compared with the target torque variation amount, all the torque variation amounts obtained before the engine operating condition changes are reset to zeros. After all the torque variation amounts are reset, the torque variation amount cannot be obtained until the interchange torque variations amounts for the predetermined number of cycles in the changed (new) engine operating condition are obtained. Hence, it is impossible to accurately control the torque variation until the predetermined number of cycles elapse.